The invention relates to blanks made from zeolite which adsorb and desorb an adsorbed substance and a process for making the same.
Zeolite crystals adsorb liquid and gaseous adsorbed substances under heat development. The released reaction heat must be dissipated from the zeolite material during the adsorption and must again be fed thereto during the desorption (separation of both substances). The reaction kinetic of the adsorption and desorption process is limited by a low heat conductivity of zeolite mass and by high pressure drops of the adsorbed substance which either flows thereto or therefrom.
The diameter of synthetic zeolite crystals is limited to a few micrometer. Powder fillings are not suitable for technical absorbing processes, since the fine zeolite crystals are subjected to turbulence and are carried out from the reaction spaces by the flow of the adsorbed substances. A further processing of the powderlike zeolite products in specific but expensive granulating processes by adding of binders in granulate, for example, small balls or cylinder permits the use of zeolite in drying processes. In these processes moist gases flow through the granulate fillers and emit the moisture to the granulate fillers. In this manner the dry gases absorb the generated reaction heat and cool the granulate. Hot and dry gases are fed in the subsequent process step for desorption of the granulate fillers. They transmit the reaction heat to the granulate and absorb the released moisture. In these so-called open processes the gases flow around each granulate body. The total surface of the granulate body is available for the heat exchange.
Zeolite granulates for the adsorption of steam in adsorption heat pumps and air conditioners are suggested in a plurality of patent applications. There the zeolite crystals adsorb steam in a closed process. Gas flows which could transmit the reaction heat are not available. The heat must be fed and dissipated from the outside by specific heat exchangers. The heat can only be transmitted via the contact faces of the granulate fillers. Therefore, the heat transmission is not dependent on the granulate surface but from the number of contact locations of the granulates among each other and with respect to the heat exchanger. Hence, the heat conductivity is therefore lower with fillers than with homogenic substances. The flow resistance is higher than in comparable flow conduits with smooth surfaces.
The DE No. 3 207 656 A1 suggests zeolite blanks which are adapted to the heat exchanger surfaces and which are provided with flow conduits that are most favorably designed for the adsorbed substance. After only a few desorption cycles the zeolite blanks detach from the heat exchanger surfaces. Thin slots are created which limit the heat transfer even more severely than with granulate fillers. Severely fluctuating temperature and load gradients generate cracks and slots within the blanks which additionally lower the heat conductivity. Broken-off zeolite parts block the flow conduits and prevent the access of the adsorbed substance to the zeolite.